Compare Two Raw Vectors Without Leaking Timing Information

Compares in time that does not depend on the contents of the buffers. Use it whenever one side is a secret: an authentication tag, a password verifier, a derived key.

Usage

crypt_equal(x, y)

Arguments

x, y

Raw vectors.

Value

TRUE if the vectors have the same length and the same contents, otherwise FALSE.

Length is not hidden

Vectors of different lengths return FALSE immediately, without comparing anything. Hiding a length difference is not something a comparison function can do, and pretending otherwise would be worse than saying so: if the length of your secret is itself secret, compare digests of the values rather than the values.

Examples

a <- crypt_hash(charToRaw("message"))
b <- crypt_hash(charToRaw("message"))
crypt_equal(a, b)
#> [1] TRUE

crypt_equal(a, crypt_hash(charToRaw("different")))
#> [1] FALSE

# Different lengths are simply not equal.
crypt_equal(a, raw(0))
#> [1] FALSE